<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		
		<script>
			// 1.undefined(未定义):当一个变量进行了声明,但是没有赋值,这个时候它的值就是undefined
			var flag;
			console.log(flag);//目前的值是undefined
			console.log(typeof flag);//类型是undefined
			
			// 2.null(空):
			var info = {name: "why", age: 18};
			info = null;
			
			console.log(undefined == null); //true
		</script>
	</body>
</html>
